The broad, long-term objectives of this application are to develop methods to predict and treat diurnal and long-term residual limb shape changes to reduce the occurrence of skin breakdown in persons with lower-limb amputation. The specific aims are to assess interface-stress stability in trans-tibial amputee subjects under different socket-modification treatments designed to overcome fit problems induced by shape changes. A further aim is to better understand the sources of diurnal and long-term shape changes and to correlate them with residual limb fluid transport and other patient tissue characteristics that can be assessed in clinical evaluation. To address the aims fluid-filled cells at controlled volumes, a uniform-thickness insert, and material patches affixed to the inside of the socket at locations of soft-tissue loss are used with an existing interface pressure and shear stress measurement system and a custom, high-resolution, residual-limb scanner. The capabilities of the treatments to keep interface stresses consistent over both diurnal and 12-mo intervals, despite changes in residual limb shape, are determined and compared with no treatment. It is expected that for diurnal fluctuations: the fluid-filled cells perform better than the other treatments; the optimal cell fluid volume to keep interface stresses consistent matches the residual limb volume loss; and using the fluid cells distal limb movement in the socket is identical to that of the initial fit. For long-term changes, it is expected that both local material patches affixed to the inside of the socket and the fluid-filled cells are needed to stabilize interface stresses. To better understand the physiologic sources of residual limb shape change, residual limb extracellular water content, fluid transport, and tissue content are measured on a population of trans-tibial amputee subjects. It is expected that diurnal shrinkage reflects a slow loss of extracellular water over the course of the day. Long-term shrinkage, however, is expected to reflect a reduction in muscle tissue content. The health relatedness of this project is improvement in the quality of life of persons with amputated limbs. The development of methods to predict and overcome the detrimental effects of residual limb shape change and ultimately prevent soft-tissue breakdown will help to prevent secondary disability and morbidity in the amputee population.